The present invention relates to a low frequency power converter and specifically to low frequency electronic ballasts for gas discharge devices. More specifically, the present invention relates to a low frequency square wave electronic ballast for high intensity discharge (HID) lamps.
The prior art is replete with many known circuits providing electronic ballast for gas discharge lamps. For instance, high efficient electronic ballast which can be used with HPS (HID) lamps are discussed in U.S. Pat. No. 5,313,143 entitled “Master-slave half-bridge DC-to-AC switchmode power converter”, and U.S. Pat. No. 6,329,761 entitled “Frequency controlled half-bridge inverter for variable loads”, from the same inventor of the present invention. Furthermore, a low frequency square wave electronic ballast, especially for metal halide (MH) lamps are discussed in U.S. Pat. No. 5,428,268, entitled “Low frequency square wave electronic ballast for gas discharge devices”, also from the same inventor of the present invention. The present invention has several basic differences if compared to the previously mentioned low frequency square wave ballast.
Introduction of a new solution for zero current sensing (which is an important functional part for both the input and current source units), a simple temperature compensated nonlinear function generator, the implementation logic supplies for the floating switches of the low frequency full-bridge inverter are among the main improvements and a more effective ignition solution. Further low frequency electronic ballast are discussed in U. S. Pat. No. 5,710,488 entitled “Low-frequency high-efficacy electronic ballast”, from Nilssen, U.S. Pat. No. 4,614,898 entitled “electronic ballast with low frequency AC to AC converter” from Itani et al, 1986, U.S. Pat. No. 6,166,495 entitled “square wave ballast for mercury free arc lamp”, from Newell et al, and U.S. Pat. No. 5,235,255 entitled “Switching circuit for operating a discharge lamp with constant power” from Blom. Still further advantages of the present invention comparing to mentioned patent applications will become apparent from a consideration of the ensuing description and drawings.
An important application for high frequency switchmode power converters is supplying power to gas discharge devices, especially high intensity discharge (HID) lamps. Therefore, the efficiency of the conventional core&coil ballast can be significantly improved and the weight decreased. In the case of high frequency powering of gas discharge lamps, the high frequency ballast and the gas discharge lamp have a higher level of interaction than that which exists between a conventional low frequency ballast and gas discharge lamp. High frequency ballasts, where the frequency of lamp current higher than 4 kHz, may suffer from acoustic resonance which can cause various problems such as instability, high output fluctuation, or, in the worst case, cracked arc tubes. Therefore, an optimum solution to this problem is the use of a high frequency DC-to-DC switch-mode converter as a controlled current source connected to a low frequency DC-to-AC square wave inverter supplying the gas discharge lamp. Due to its lessened weight, higher efficiency and the nonexistence of flickering and acoustic resonances, this novel high frequency ballast providing low frequency square wave current for the HID lamps, has significant advantages when compared with either the conventional low frequency ballasts and the usual high frequency electronic ballast. Additionally, a new, high sophisticated electronic ballast generation can be introduced to provide several special features, such as, for example, automatic or controlled dimming providing significant energy saving in a wide temperature range.